I just received my K-7 this week, so I don't have a lot to go on... (and I wonder why I didn't buy it sooner)
I am coming from the K200D and KM. Pixel Peeping (which I don't do too often), I would say noise is similar, if not better on the K-7. (BTW, I always shoot RAW) I'd say up to ISO 1250, maybe 1600, I probably wouldn't even bother with a noise reduction program outside of Lightroom. 1600+, needs some noise reduction, but not a great deal as the noise is not intrusive to the photograph. What I mean by that is , even at higher ISO's, the level of detail retained is better than I have ever seen from a DSLR (or any camera for that matter).
I've been reading a lot of complaints about the noise recently (even more so now the K-X is out), but in reality, I think it is
VERY exaggerated. Probably by more non-users than users. I have no issues shooting at anything up to ISO 1600. I'd even go above that in ceratin situations. That is OK in my book. Heck, my favorite DSLR (and the K-7 is giving it a run for its money) is the Olympus E-1. On the E-1, ISO 400 was about as high as you'd want to go (800 in a pinch).
My point is, you learn to live with different shortcomings, because (hopefully) the advantages outweigh the disadvantages. And this is where personal preferences come into play. I may feel a super quiet shutter, 5 FPS, and weather sealing are more important than a clean ISO 3200. You may feel that that shooting at ISO 3200 all night long is something you need. I have searched for the perfect camera (and camera system), but it doesn't exist. In my perfect world, I'd have a K-7 with every limited ever made, a D700 with some fast primes to take advantage of low light and extreme DOF, and an E-3 with some fantastic Olympus zooms to utilize the 2x crop factor. However, I am not a rich person, so I have to decide what is best for me at this time. I think I have found it.
Back to noise, I plan on making some K-7 prints to see how *bad* this camera actually is...
I have a feeling that in prints of 16x20 or less, you'd be hard pressed to see any noise equal to or under ISO800, maybe even higher. And when printing larger or at higher speeds, I imagine the noise would look more like grain because of the detail in the shot.